CLASS INSECTS. 



397 



These last present even a remarkable peculiarity; for in 

 general insects change their skin for the last time when they 

 pass from the stage of nymph to their perfect state, whilst 

 the ephemera experiences another moulting before becoming 

 completely adult, although in this state it lives but a few 



Fig. 376, Ephemera. 



hours. The larva of this ephemera lives in water, and differs 

 but little from the adult, excepting in the shortness of its 

 limbs, the absence of wings, and by the row of laminae or 

 plates which it has on each side of the abdomen, and which 

 it employs as organs of respiration and of swimming. The 

 nymph (Fig. 377), only differs from the larva by 

 the presence of sheaths enclosing the wings. At 

 the moment when these organs are to be de- 

 veloped, the insect quits the water, and after 

 having vaulted in the air for some minutes, pro- 

 ceeds to rest upon an elevated object, when it 

 abandons itself to violent movements, by means 

 of which it throws off its tegumentary membrane; 

 it is then only that its limbs acquire all their length, 

 and its body the colours it is afterwards to preserve. 

 535. Some insects, although they undergo 

 considerable changes when young, do not pass 

 through the complete series of transformations of 

 which we have just spoken ; they seem, as it were 

 to stop en route, and never come to possess 

 wings. Fleas are in this case, and. leaving Fj g . 377. 

 the egg, they have no feet, and have the form 

 of small worms, of a whitish colour. These larvae are very 

 lively, and roll themselves into a circle or spiral. Soon 

 they become reddish, and after having lived in this state a 

 dozen days, they shut themselves up in a small silky cocoon of 

 extreme fineness, to be transformed into a nymph ; then, at 



